Multiplexing of trim outputs on a trim bus to reduce die size

ABSTRACT

An integrated circuit includes trim circuitry to control operations of internal circuitry. The integrated circuit includes multiplex circuitry for coupling the trim circuitry to internal circuits via a trim bus in a manner which reduces die area. The trim circuitry is controlled such that fuses used to control different level and timing parameters are grouped together and routed across the integrated circuit using the trim bus and multiplex circuit.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to static information storage and in particular the present invention relates to multiplexing trim circuits.

BACKGROUND OF THE INVENTION

[0002] Also, many processor systems which operate with an associated memory require a particular memory configuration to operate properly. By way of example, some systems require a word length of eight bits and some require sixteen bits. There are conventional memory systems available which permit the end user to control the word size to some degree. However, this somewhat increases the complexity imposed upon the end user of the memory since the end user must provide the necessary signals to the memory for controlling the word length. As a further example, most processor systems look to a certain portion of a memory for boot data at power on. Such boot data is necessary for the processor to function in system. The processor will be implemented to expect the boot data to be at a specific memory address. Some processors expect the boot data to be at the memory low addresses (bottom boot) and some processors expect the boot data to be at the memory high addresses (top boot). In order to provide capabilities for different types of processor systems, it is possible to produce a different memory system for each application. However, it is always desirable to limit the number of different memory types which must be manufactured.

[0003] It is desirable to have a memory system which can be fully characterized after fabrication. See for example U.S. Pat. No. 5,627,784 entitled “Memory System Having Non-Volatile Data Storage Structure for Memory Control Parameters and Method” which is incorporated herein for a description of a memory which uses non-volatile data storage units for controlling parameters of the memory device. These non-volatile data storage units are typically located in a common area on the integrated circuit and are coupled to circuitry which is located throughout the integrated circuit. The interconnect system is both complex and requires substantial die area.

[0004] For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a memory which uses data storage units for controlling parameters of the memory device and reduces die area by multiplexing control signals.

SUMMARY OF THE INVENTION

[0005] The above mentioned problems with routing control signals and other problems are addressed by the present invention and will be understood by reading and studying the following specification.

[0006] In particular, the present invention describes an integrated circuit comprising trim circuitry which provides output signals to control operations of internal circuitry. The trim circuitry includes a plurality of non-volatile fuse adapted to provide X trim signals. A trim bus is selectively coupled to the trim circuitry for routing the X trim signals across the integrated circuit. The trim bus comprises Y interconnect lines, where Y is greater than X. Multiplex circuitry is provided for coupling a group of Y trim signals selected from the X trim signals of the trim circuitry to internal circuits via the trim bus.

[0007] Another aspect of the invention provides a flash memory device comprising trim circuitry which provides output signals to control operations of internal circuitry. The trim circuitry includes a plurality of non-volatile memory cells adapted to provide X trim signals. A trim bus is selectively coupled to the trim circuitry for routing the X trim signals across the flash memory device, the trim bus comprising Y interconnect lines, where Y is greater than X. Further, multiplex circuitry is provided for coupling a group of Y trim signals selected from the X trim signals of the trim circuitry to internal circuits via the trim bus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a block diagram of a flash memory incorporating the present invention;

[0009]FIG. 2 is a more detailed illustration of the memory of FIG. 1;

[0010]FIG. 3 is a block diagram of an integrated circuit incorporating the present invention;

[0011]FIG. 4 illustrates one embodiment of a multiplex circuitry;

[0012]FIGS. 5A and 5B illustrates one embodiment of a high voltage trim multiplex circuit;

[0013]FIGS. 6A and 6B illustrates one embodiment of a sense/pulse trim multiplex circuit; and

[0014]FIGS. 7A and 7B illustrates one embodiment of a high current trim multiplex circuit.

DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific preferred embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present inventions. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

[0016] The present invention provides a memory which multiplexes trim circuitry that controls parameters of the memory to reduce die area. Prior to describing these features in greater detail, a brief description of a flash memory of the present invention is provided.

Flash Memory

[0017]FIG. 1 illustrates a block diagram of a Flash memory device 100 which is coupled to a flash controller 102. The memory device has been simplified to focus on features of the memory which are helpful in understanding the present invention. The memory device 100 includes an array of memory cells 104, FIG. 2. The memory cells are preferably floating gate memory cells. The array is arranged in rows and columns, with the rows arranged in blocks. The blocks allow memory cells to be erased in large groups. Data, however, is stored in the memory array in small data groups (byte or group of bytes) and separate from the block structure. Erase operations are performed on a large number of cells in parallel.

[0018] An x-decoder 108 and a y-decoder 110 are provided to decode address signals provided on address lines A0-Ax 112. Address signals are received and decoded to access the memory array 104. An address buffer circuit 106 is provided to latch the address signals. A y-select circuit 116 is provided to select a column of the array identified with the y-decoder 110. Sense amplifier and compare circuitry 118 is used to sense data stored in the memory cells and verify the accuracy of stored data. Data input 120 and output 122 buffer circuits are included for bi-directional data communication over a plurality of data (DQ) lines with the microprocessor 102. Command control circuit 114 decodes signals provided on control lines from the microprocessor. These signals are used to control the operations of the memory, including data read, data write, and erase operations. Input/output control circuit 124 is used to control the input and output buffers in response to some of the control signals. The flash memory includes a charge pump circuit 123 which generates a Vpp voltage used during programming of the memory cells and other internal operations. During write operations, Vpp is coupled to the memory cells for providing appropriate write operation programming power. Charge pump designs are known to those skilled in the art, and provides power which is dependant upon an externally provided supply voltage Vcc.

[0019] Latch circuitry 125 is provided in the memory for latching locations of memory cells which are not successfully written to during a memory write operation. The latch circuitry allows rewrite operations, as described below, to be performed after a plurality of separate memory write operations are performed.

[0020] As stated above, the Flash memory of FIGS. 1 and 2 has been simplified to facilitate a basic understanding of the features of the memory. A more detailed understanding of Flash memories is known to those skilled in the art. It will be appreciated that more than one Flash memory can be included in various package configurations. For example, Flash memory cards can be manufactured in varying densities using numerous Flash memories.

Trim Circuitry

[0021]FIG. 3 illustrates a block diagram of an integrated circuit 200, such as a memory device, incorporating the present invention. The integrated circuit includes trim circuitry 202 which provides output signals to control operations of internal circuitry. Because the trim circuitry includes non-volatile memory it is best suited for use in memory circuits and the trim circuitry is fabricated in close proximity to a memory array. The integrated circuit includes multiplex circuitry 204 for coupling the trim circuitry to internal circuits 206 via a trim bus and control 208 in a manner which reduces die area. That is, trim circuitry is controlled such that fuses used to control different level and timing parameters are grouped together and routed across the integrated circuit using the trim bus and multiplex circuit.

[0022] A description of a memory device with control parameters using non-volatile storage is described in U.S. Pat. No. 5,627,784 issued May. 6, 1997 and entitled “MEMORY SYSTEM HAVING NON-VOLATILE DATA STORAGE STRUCTURE FOR MEMORY CONTROL PARAMETERS AND METHOD”. U.S. Pat. No. 5,682,345 issued Oct. 28, 1997, entitled “NON-VOLATILE DATA STORAGE UNIT AND METHOD OF CONTROLLING SAME” describes a non-volatile unit for storing control parameters. Each of the above references are incorporated herein, and provide a description of the trim fuses and there intended uses.

[0023] Referring to FIG. 4, control signals from the trim circuitry are routed using multiplex circuits 210, 212 and 214. The control signals in the integrated circuit memory device includes a three bit bus, ErsMarg<3:1>, used to adjust the level of the current of the sense amplifier for verifying if a cell is erased properly. A two bit bus, HealWL<2:1>, is used to adjust a voltage level of wordlines during a Heal operation after an erase cycle. A three bit bus, PgMarg<3:1>, is used to adjust the level of the current of the sense amplifier for verifying if a cell is programmed properly. A three bit bus, PgmWL<3:1>, is used to adjust the level of the voltage on a wordline during programming operation. Likewise, SoftPWL<2:1> is a two bit bus used to adjust the level of the voltage on a wordline during soft programming operation. This operation is used to recover from over-erased cells.

[0024] This first group of trim fuse outputs are all associated with voltages related to wordlines during high voltage operations and settings which relate to sense amplifier operations. It is important to note that these trim settings are not required at the same time. For example, high voltage operations may be performed first, and then verification operations are performed to determine if an operation was successful using the sense amplifiers. Therefore, these fuse element outputs are placed on the same bus.

[0025] A second group of trim circuit outputs include a two bit bus, SPMarg<2:1>, used to set soft programming current levels in the sense Amplifiers. A three bit bus, SenMarg<3:1>, includes output of three fuse elements that are used to set the level of verification of the sense amplifier during a normal read operation. A three bit bus, PgmPls<3:1>, provides output of three fuse elements that are used to set the duration of the programming pulse. Likewise, a HealPls<2:1> bus provides output of two fuse elements that are used to set the duration of a heal pulse during a heal operation performs after an erase cycle to recover from over-erasure. Finally, HErPls<2:1> provides output of two fuse elements that are used to set the duration of the erase operation after a Heal operation to recover any inadvertently reduced margin of some erased cells. The above described second set of trim element signals are mostly related to sense amplifier outputs.

[0026] The third group of trim signals include a three bit bus, ErsSrc<3:1>, used to set a voltage level on the sources of a memory cells being erased. A three bit bus, PgmBL<3:1>, is provided to set a voltage level on bit lines during a programming operation, and a three bit bus, SoftPBL<3:1>, is provided to set a voltage level on the bit lines during a soft programming operation.

[0027] The multiplex circuitry 210, 212 and 214 of one embodiment of the present invention routes the 34 control signals from the trim circuitry over nine bus lines. Thus, where prior integrated circuits required 34 metal lines routed around the integrated circuit from the trim location to control different circuits, the present invention uses nine lines.

[0028]FIGS. 5A and 5B illustrate one embodiment of a high voltage trim multiplex circuit 210 used with the above described first signal group. Seven control signals are used to couple the trim fuses to an internal bus. The signals include an ActiveHV to indicate when the memory is performing High voltage operations within a program or erase operation. A HealCyc signal indicating the performance of a Heal cycle of a memory erase operation. The Program Margin Enable signal, PgMargE, signifies that any reading of the memory array should be performed to verify that the cell has sufficient programming margin. A PgmOp signal is used to indicated that the memory is either in programming mode or pre-programming mode within an erase operation. A SoftPgm signal indicates the execution of a soft programming cycle used in over-erased memory cell threshold recovery. An ErsCyc signal is provided which signifies that the memory is in a cell erase cycle within an erase operation. Finally, a TstOvrWrt signal is used to overwrite the output of all the fuse elements to a known state.

[0029] The multiplex circuitry of FIG. 5A couples either the PgmvWL<3:1>, HealWL<2:1>, SoftPWL<2:1>, PgMarg<3:1>, or ErsMarg<3:1> trim output signal to the high voltage bus. Each of the trim output signals is coupled to the bus via isolation devices 220, or transistors, controlled by logic circuits 222. The logic expression used to activate the isolation devices for the PgmWL trim signals is:

{overscore ((PgmOP+ErsCyc)*ActiveHv*)}{double overscore (Softpgm)}

[0030] The logic expression used to activate the isolation devices for the HealWL trim signals is:

{overscore (ActiveHV*Healcyc)}

[0031] The logic expression used to activate the isolation devices for the SoftPWL trim signals is /SoftPgm. The logic expression used to activate the isolation devices for the PgMarg trim signals is:

{double overscore ((ActiveHV+Softpgm))}{overscore (*PgmargE)}

[0032] The logic expression used to activate the isolation devices for the ErsMarg trim signals is:

{double overscore ((ActiveHV+Softpgm))}{overscore (*)}{double overscore (PgmargE)}

[0033] Because the HealWL<2:1> and SoftPWL<2:1> trim signals are two bits, while the bus is three bits, one line of the bus is coupled to ground by the appropriate isolation device. The multiplex also includes a test overwrite circuit 224 which uses the TstOvrWrt signal to couple the bus lines to a trim bus. Two coupling logic circuits are illustrated; one using a NOR gate 226 and one using a NAND gate 228. When the TstOvrWrt signal is in a low state, the bus lines are coupled to the trim bus. When the TstOvrWrt signal is in a high state, the trim bus connections are coupled low.

[0034]FIGS. 6A and 6B illustrate one embodiment of a sense/pulse trim multiplex circuit 212 used with the above described second signal group. Logic circuit 230 is provided to couple the signal group to bus via isolation devices 231. In addition to some of the above control signals, an additional control signal, SPMargE, is used to indicate that currents read out of memory cells are for soft program margin purposes. When the memory device is in an active high voltage mode, the soft program margin signal trim signals, SPMarg<2:1>, and the sense amplifier verification level, SenMarg<3:1>, are not coupled to the sense/pulse bus. Conversely, during the high voltage operation, the PgmOp, HealCyc, and ErsCyc signals control the coupling of PgmPls<3:1>, HealPls<2:1>, and HerPls<2:1> trim signals to the sense/pulse bus, respectively.

[0035] The multiplex of FIG. 6B also includes a test overwrite circuit 232 which uses the TstOvrWrt signal to couple the bus lines to a trim bus. Bus lines one and three are coupled through a NAND gate 234, and bus line 2 is coupled though a NOR gate 236. A latching inverter 240 is provided to latch the third bus line.

[0036]FIGS. 7A and 7B illustrates a multiplex circuit 214 used to couple either PgmBL<3:1>, ErsSrc<3:1>, or SoftPBL<3:1> to a three bit high current bus. The multiplex circuitry couples PgmBL<3:1> to the three bit bus in response to a low ErsCyc and a low Softpgm signals via NOR gate 241 and transfer circuitry 242. The ErsSrc<3:1> signal is coupled to the bus when the ErsCyc signal is high via transfer circuit. Finally, the SoftPBL<3:1> is coupled to the bus when the Softpgm signal is high using transfer circuit. The multiplex of FIG. 7B also includes a test overwrite circuit 244 which uses the TstOvrWrt signal. Bus lines 1 and 3 (HCTrim<3,1>) are coupled through NAND gate 246, and bus line 2 is coupled though NOR gate 248. Thus, when the TstOvrWrt signal is high bus line 2 is coupled low, and bits lines 1 and 3 are coupled high. When the TstOvrWrt signal is low, the bus data is not over written.

Conclusion

[0037] An integrated circuit has been described which includes trim circuitry to control operations of internal circuitry. Because the trim circuitry includes non-volatile memory it is well suited for use in memory circuits. The integrated circuit includes multiplex circuitry for coupling the trim circuitry to internal circuits via a trim bus in a manner which reduces die area. The trim circuitry is controlled such that fuses used to control different level and timing parameters are grouped together and routed across the integrated circuit using the trim bus and multiplex circuit.

[0038] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof. 

What is claimed is:
 1. An integrated circuit comprising: trim circuitry which provides output signals to control operations of internal circuitry, the trim circuitry includes a plurality of non-volatile fuse adapted to provide X trim signals; a trim bus selectively coupled to the trim circuitry for routing the X trim signals across the integrated circuit, the trim bus comprising Y interconnect lines, where Y is greater than X; and multiplex circuitry for coupling a group of Y trim signals selected from the X trim signals of the trim circuitry to internal circuits via the trim bus.
 2. The integrated circuit of claim 1 further comprising a control circuit for controlling the multiplex circuitry to select the Y trim signals from the X trim signals in response to an operational state of the integrated circuit.
 3. The integrated circuit of claim 1 wherein the multiplex circuitry comprises a plurality of multiplex circuits for coupling a group of Y trim signals selected from the X trim signals.
 4. The integrated circuit of claim 1 wherein the integrated circuit is a flash memory device and the multiplex circuitry comprises a first multiplex circuit for coupling a group of Y trim signals related to controlling word lines during high voltage operations and settings which relate to sense amplifier operations.
 5. The integrated circuit of claim 4 wherein the multiplex circuitry comprises a second multiplex circuit for coupling a group of Y trim signals related to sense amplifier outputs.
 6. The integrated circuit of claim 1 wherein Y is at least three times greater than X.
 7. A flash memory device comprising: trim circuitry which provides output signals to control operations of internal circuitry, the trim circuitry includes a plurality of non-volatile memory cells adapted to provide X trim signals; a trim bus selectively coupled to the trim circuitry for routing the X trim signals across the flash memory device, the trim bus comprising Y interconnect lines, where Y is greater than X; and multiplex circuitry for coupling a group of Y trim signals selected from the X trim signals of the trim circuitry to internal circuits via the trim bus.
 8. The flash memory device of claim 7 farther comprising a control circuit for controlling the multiplex circuitry to select the Y trim signals from the X trim signals in response to an operational state of the memory device.
 9. The flash memory device of claim 7 wherein the multiplex circuitry comprises three multiplex circuits.
 10. The flash memory device of claim 9 wherein the multiplex circuitry comprises a first multiplex circuit for coupling a first group of trim signals related to high voltage operations.
 11. The flash memory device of claim 10 wherein the first group of trim signals comprises: a three bit erase margin signal; a two bit heal word line signal; a three bit program margin signal; a three bit program word line signal; and a two bit soft program word line signal.
 12. The flash memory device of claim 9 wherein the multiplex circuitry comprises a second multiplex circuit for coupling a second group of trim signals related to sense amplifier operations.
 13. The flash memory device of claim 12 wherein the second group of trim signals comprises: a two bit soft program margin signal trim signal; a three bit sense amplifier verification level signal; a three bit program pulse signal; a two bit heal pulse signal; and a two bit heal erase pulse signal.
 14. The flash memory device of claim 9 wherein the multiplex circuitry comprises a third multiplex circuit for coupling a third group of trim signals related to high current operations.
 15. The flash memory device of claim 14 wherein the third group of trim signals comprises: a three bit memory source voltage signal, used during erase operations; a three bit line voltage signal, used during programming operations; and a three bit line voltage signal, used during soft programming operations.
 16. The flash memory device of claim 7 wherein the multiplex circuitry comprises overwrite circuitry for decoupling outputs of the multiplex circuitry from the trim bus in response to a test signal.
 17. The flash memory device of claim 7 wherein the X trim signals comprise 34 trim signals and the trim bus comprises nine interconnect lines.
 18. A method of reducing interconnect routing in a flash memory device using non-volatile trim circuits, the method comprising: providing trim signals from the non-volatile trim circuits; selecting a predetermined number of the trim signals based upon an operating state of the flash memory device; and multiplexing the selected trim signals on common bus lines provided on the flash memory device.
 19. The method of claim 18 further comprising decoupling outputs of multiplex circuitry from the common bus lines in response to a test signal.
 20. The method of claim 18 wherein the trim signals are multi-bit signals. 